The flue ash which collects in coal power plants is used in the cement industry to produce ash cement. More flue ash accumulates in the winter months than in the summer months, while more cement is produced in the summer months than in the winter months. For this reason large silos must receive the ash production of the winter months so that it is avalable in the summer months. However, problems occur in the storage of flue ash, because flue ash is hygroscopic. Although it flows quite readily in a dry state when being stored, it solidifies so much after a certain storage time that it can hardly be economically returned to a flowable state with pneumatic means. Therefore, mechanical conveyors are used in known large-capacity silos for removing the ash which can be moved both radially and horizontally on the surface of the stored material on a carrier structure. These conveyors convey the material loosened from the surface from the outside to the center to a hollow control column where it is caught by a shovel scraper which revolves at the circumference of the column. The scraper then pushes the material circularly around the column until it can exit at one of the openings in the column to the hollow space in the column. Several openings are distributed over the height of the column, each of which is closed by a slide. These slides are opened in succession from the top down, depending on the degree of filling of the silo. When the silo is being filled, the slides are closed easily, so that the hollow space in the column is not completely filled.
The known arrangement has the disadvantage that the expense for the slides is great and that the wear on the shovel scraper which pushes the material circularly around the central column is very great, since flue ash is extremely abrasive.